Ferrite circulators for waveguides circulate radio frequency (RF) power from one port to another port while absorbing a minimal amount of the circulating power. All of the dielectric and ferrite materials in circulators absorb some power, but the majority of the power absorbed by a ferrite circulator is contained in the ferrite element due to the relatively high volume of the ferrite element, as well as the relatively high electrical and magnetic loss tangents of the ferrite material.
In conventional single junction waveguide circulators, the ferrite temperature rise resulting from the power absorption is primarily dependent on the thermal resistance of the various paths from the ferrite element to the thermally conductive waveguide structure. The waveguide structure acts as a heat sink for the ferrite element, but the thermal paths between these two parts are limited in conventional circulators. These thermal paths flow from the ferrite element through adhesive bonds to either dielectric spacers or quarter-wave dielectric transformers, and on through adhesive bonds to the waveguide structure. The dimensions of the dielectric spacers and quarter-wave dielectric transformers are restricted by RF performance requirements rather than thermal requirements.
Some prior circulators incorporate thermally conductive dielectric attachments in order to maximize the area of contact with the ferrite for improved heat transfer, thereby allowing ferrite circulators to operate at higher average microwave power levels. Nevertheless, increasing average power requirements provide the need for improving the average power handling of ferrite circulators such as switching circulators.